An Analysis Of The Effect Of 3-D Groove Insert Design On Chip Breaking .
An Analysis of The Effect of 3-D Groove Insert Design on Chip Breaking Chart by Alfred Avanessian A Thesis Submitted to the faculty of WORCESTER POLYTECHNIC INSTITUTE in partial fulfillment of the requirements for the Degree of Master Science in Manufacturing Engineering by Alfred Avanessian, January 2005 APPROVED: Yiming (Kevin) Rong, Advisor, Professor of Mechanical Engineering, Associate Director of Manufacturing and Materials Engineering
Abstract Prediction of chip-breaking in machining is an important task for automated manufacturing. There are chip-breaking limits in machining chip-breaking chart, which determine the chip-breaking range. This thesis presents a study of the effect of 3-D groove insert parameters on chip breaking chart. Based on the chip-breaking criteria, the critical feed rate is formulated through an analysis of up-curl chip formation for 3-D grooves. Also in order to predict chip-breaking limits, for protruded insert grooves in finish machining, analytical models are established. In the analytical models, minimum and maximum depth of cut are identified for using different chip breaking models. As well insert nose radius effects on chip thickness for small depth of cut are studied. In the end, the analytical critical feed rate model is extended to finish machining with 3-D chipbreaking grooves. i
Acknowledgment This thesis is more than the product of the last couple of years of research and thought. It represents the coming together of many influences over quite a few years and the encouragement of fine friends, family, colleagues, and teachers past and present. I would like to thank the following people: My advisor, Professor Yiming Rong, for his guidance and support throughout my years at WPI. His critical review of the manuscript, patience and expertise helped me find direction in many areas of research related activities. I also wish to thank the other committee members, including Professor Richard D. Sisson Jr., Professor Mustafa Fofana and Dr. Hui Song for their useful comments and contributions on improving my writing style. Professor Christofer A. Brown and Mr. Torbjorn Bergstrom, The Surface Metrology Laboratory Manager, for allowing and helping me to use facilities to take measurements on some inserts. Dr. William C. S. Weir, Robotics Lab Manager and Mr. Steve Derosier and Todd Billings Haas Technical Education Center Technicians for providing machining facilities. My two-semester tuition provided by GE and WPI and Mr. Siamak M. Najafi for providing on campus job are also acknowledged. The members of the CAM Lab at WPI and Mohamed C. Shaw all provided companionship and made fun in addition to providing valuable scholarly input to this work. Finally, I would like to dedicate this thesis to my parents and siblings for their constant love, moral and financial support during my studies. ii
Nomenclature bch Chip width (mm), (in) bγ1 Insert/chip restricted contact length (mm), (in) Ch Cutting ratio (the ratio of the undeformed chip thickness to the chip thickness) d Depth of cut (mm), (in) d0 The standard critical depth of cut under pre-defined standard cutting condition (mm), (in) dmax Maximum depth of cut in extra region of chip-breaking chart (mm), (in) dmin Minimum depth of cut in extra region of chip-breaking chart (mm), (in) f Feed rate (mm/rev), (in/rev) f0 The standard critical feed rate under pre-defined standard cutting condition (mm/rev), (in/rev) fcr The critical feed rate (mm/rev), (in/rev) fcr The critical feed rate (mm/rev), (in/rev) h Insert backwall height (mm), (in) hch Chip thickness (mm), (in) Kdbr1 Modification coefficient of the cutting tool (insert) land length effect on the critical depth of cut Kdkr Modification coefficient of the insert lead angle effect on the critical depth of cut Kdm Modification coefficient of the workpiece material effect on the critical depth of cut Kdrε Modification coefficient of the cutting tool (insert) nose radius effect on the critical depth of cut KdT Modification coefficient of the cutting tool (insert) effect on the critical depth of cut KdV Modification coefficient of the cutting speed effect on the critical depth of cut KdWn Modification coefficient of the cutting tool (insert) chip-breaking groove width effect on the critical depth of cut Kdγ0 Modification coefficient of the cutting tool (insert) rake angle effect on the iii
critical depth of cut Kdγ01 Modification coefficient of the cutting tool (insert) land rake angle effect on the critical depth of cut Kfbr1 Modification coefficient of the cutting tool (insert) land length effect on the critical feed rate Kfh Modification coefficient of the cutting tool (insert) backwall height effect on the critical feed rate Kfh Modification coefficient of the cutting tool (insert) backwall height effect on the critical depth of cut Kfkr Modification coefficient of the insert lead angle effect on the critical feed rate Kfm Modification coefficient of the workpiece material effect on the critical feed rate Kfrε Modification coefficient of the cutting tool (insert) nose radius effect on the critical feed rate KfT Modification coefficient of the cutting tool (insert) effect on the critical feed rate KfV Modification coefficient of the cutting speed effect on the critical feed rate KfWn Modification coefficient of the cutting tool (insert) chip-breaking groove width effect on the critical feed rate Kfγ0 Modification coefficient of the cutting tool (insert) rake angle effect on the critical feed rate Kfγ01 Modification coefficient of the cutting tool (insert) land rake angle effect on the critical feed rate KR Coefficient related to the chip radius breaking lb Backwall length (mm), (in) lf Chip / insert contact length (mm), (in) ln Rake face length (mm), (in) R0 Chip up-curl radius (mm), (in) RL Chip-breaking radius (mm), (in) rp Protruded nose radius (mm), (in) Rs Side curl chip radius (mm), (in) rε Insert nose radius (mm), (in) V Cutting speed (sfpm) iv
w The distance of center of protruded nose circle from insert nose radius center along insert symmetrical line (mm), (in) Wn Insert groove width (mm), (in) Wne Inset equivalent groove width (mm), (in) α Insert nose angle (deg) αch Chip cross-section shape coefficient γb Insert backwall angle (deg) (deg) γbe Insert equivalent backwall angle (deg) γn Insert rake angle (deg) γne Insert equivalent rake angle (deg) δ Chip scroll angle in side-curl (deg) ε Workpiece fracture strain (mm), (in) εB Chip strain (mm), (in) κr Insert lead angle (deg) η Chip back flow angle (deg) λs Insert inclination angle (deg) ψλ Chip side flow angle (deg) v
Table of Contents Abstract . . i Acknowledgment. . . ii Nomenclature. . iii Table of Contents . vii List of Figures . . . ix List of Tables. . . xii 1 2 3 Introduction. 1 1.1 Overview of Chip Formation . 1 1.2 Overview of Chip Breaking. 3 Literature Review of Chip Formation and Breaking . 8 2.1 Chip Flow. 8 2.2 Chip Curl . 12 2.2.1 Chip Up-Curl . 12 2.2.2 Chip Side-Curl . 15 2.2.3 Chip Lateral-Curl and Combination Chip Curl . 16 2.3 Chip-Breaking Criterion. 16 2.4 Li’s Work on Chip-Breaking. 19 2.4.1 Chip Breaking Chart . 19 2.4.2 Theoretical Analysis of Critical Feed Rate and Depth of Cut . 21 2.4.3 Semi-Empirical Chip-Breaking Predictive Model. 23 2.4.4 Chip Breaking Chart for Inserts with Complicated Geometry . 26 2.5 Chip-Breaking Groove & Cutting Tool Classification . 27 2.6 Existing Problems . 31 Objectives and Scope of Work. 32 3.1 Objectives. 32 vi
4 3.2 Approach. 32 3.3 Outline of Thesis . 34 Influential Parameters on 2-D and 3-D Up-Curl Dominated Chip. 36 4.1 Influential Parameters on 2-D Up-Curl Chip. 36 4.2 Influential Parameters on 3-D Up-Curl Dominated Chip. 39 4.2.1 Chip Side Flow Angle (ψλ). 39 4.2.2 Equivalent Parameters . 40 4.3 Experimental Validation . 45 4.3.1 Experiment Design. 45 4.3.2 Experimental Results . 48 4.4 5 Summary . 54 Critical Feed Rate Equation Analysis with Protruded Type Grooves. 56 5.1 Limits of Extra Chip Breaking Region. 56 5.1.1 Minimum Depth of Cut (dmin). 56 5.1.2 Maximum Depth of Cut (dmax). 57 5.2 Nose Radius Effects on Chip Thickness . 60 5.3 Analysis of Critical Feed Rate . 62 5.3.1 Theoretical Analysis of Critical Feed Rate. 63 5.3.2 Semi-Empirical Chip-Breaking Predictive Model. 64 5.4 5.4.1 Design of The Experiments . 65 5.4.2 Experimental Results . 66 5.5 6 Experimental Validation . 65 Summary . 70 Conclusion and Future Work . 72 6.1 Summary of this Research. 72 6.2 Future Work . 73 vii
6.2.1 Inserts with Block-Type Chip Breaker . 73 6.2.2 Inserts with Complicated Geometric Modifications . 75 6.2.3 Study on Ti17 Steel Chip-Breaking Chart . 75 References. 77 APPENDIX A. Measured Side Flow Angles. 87 APPENDIX B. Measured Chips . 89 APPENDIX C. Chip-Breaking Charts of Protruded Groove Inserts . 91 viii
List of Figures Figure 1-1 Chip Side Flow Angle (Stabler 1964). 2 Figure 1-2 Chip Side-Curl and Chip Up-Curl (Spaans 1971). 2 Figure 1-3 Chip Breaking in Brittle Materials. 4 Figure 1-4 Chip-Breaking of Ductile Materials (Shinojukza, 2001) . 4 Figure 1-5 Research Fields of Chip-Control (Zhou 2001). 5 Figure 1-6 Modes of Chip Breaking (Nakayama 1960) . 6 Figure 2-1 Chip Side Flow Angle (Jawahir, 1993). 9 Figure 2-2 Chip Side Flow Angle According to Colwell Theory. 10 Figure 2-3 Chip Flow Models for Machining with a Flat-Faced Tool (Jawahir 1998) . 11 Figure 2-4 Chip Back Flow Angle. 12 Figure 2-5 Chip Up-Curl Process with Grooved Cutting Tool (Li. Z 1990) . 13 Figure 2-6 Chip Radii According to Jawahir (1988-e) Theory. 14 Figure 2-7 Chip Up-curl Formation According to Zhou et al Theory (Zhou 2001-b). 15 Figure 2-8 Mechanism of Chip Side-Curl (Zhou 2001-b) . 15 Figure 2-9 Typical Chip Breaking Charts (Li, 1990) . 19 Figure 2-10 Chip Flow of Side-Curl Dominated ε-Type Chips (Zhou 2001-b) . 22 Figure 2-11 Factors Influence Chip Breaking (Zhou 2001-b) . 24 Figure 2-12 A Sample Chip Breaking Chart Produced by Complicated Groove Inserts (Zhou 2001-b) . 26 Figure 2-13 Classification of Chip Breaker / Chip-Breaking Groove (Zhou 2001-b). 28 Figure 2-14 Inserts with Three-Dimensional Chip-Breaking Groove . 29 Figure 2-15 Simple Groove Nominal Parameters and Profiles . 30 Figure 2-16 Protruded Groove Nominal Parameters . 30 Figure 4-1 Chip Formation in Long Backwall Groove. 37 Figure 4-2 Chip Formation in Insert Without Backwall. 38 Figure 4-3 Equivalent Parameters along Chip Formation . 41 Figure 4-4 Chip Side Flow Angle (ψλcr1) Indicates the Groove Width Equation Limit . 42 Figure 4-5 Groove Dimensions in Protruded Groove Type Inserts. 43 Figure 4-6 Groove Side Flow Angle Related to Effectiveness of Groove . 44 ix
Figure 4-7 Inserts Implemented in Experimental Validation . 46 Figure 4-8 Scanned Picture of CNMG432-NL92 Insert. 46 Figure 4-9 Dimensions of CNMG432-NL92 Insert along Section A-A. 47 Figure 4-10 TNMP 332K KC850 Insert with 0.03 in. Depth of Cut 0.0046 in/rev Feed Rate . 48 Figure 4-11 Produced Chip Situation on TNMP 332K KC850 Insert Groove. 49 Figure 4-12 Comparison between Avanessian and Zhou’s Models for Chip Radius Produced by TNMP 332K KC850 Insert. 49 Figure 4-13 Comparison between Avanessian and Zhou’s Models for Chip Radius Produced by CNMG432-NL92 Insert. 51 Figure 4-14 Side Flow Angle in 0.015 in/rev Feed Rate and 0.017 in. Depth of Cut . 52 Figure 4-15 Flow Chart of Influential Parameters on Up-Curl Chip. 53 Figure 5-1 Minimum Depth of Cut. 57 Figure 5-2 Machining Condition Where Groove is Ineffective. 58 Figure 5-3 Chip Section Curved Due to Groove Nose Radius (Li, 1996). 58 Figure 5-4 Maximum Depth of Cut . 59 Figure 5-5 Uncut Chip Thickness in Small Depth of Cut. 60 Figure 5-6 Uncut Chip Thickness Produced by Insert with Different Nose Radii with Different Depths of Cut . 62 Figure 5-7 Protruded Grooves Inserts Implemented in Experiment. 65 Figure 5-8 Chip Formation in 0.05 in. Depth of Cut 0.0056 in/rev Feed Rate. 67 Figure 5-9 Chip Form in Different conditions of Chip-Breaking Chart Produced by TNMG 332-QF 4025 Insert . 68 Figure 5-10 Chip Thickness in Different Depths of Cut Produced by TNMG 333-QF Insert with Different Feed Rates . 69 Figure 5-11 Chip Thickness in Different Depth of Cut Produced by TNMG 33x-QF Set Inserts with 0.0056 in/rev Feed Rate . 70 Figure 6-1 Illustration of The Geometry of The Block-Type Chip Breaker. 74 Figure 6-2 Ti17 Steel Chip-Breaking Chart. 76 Figure A-1 Depth of Cut 0.03 in. Feed Rate 0.011 in/rev . 87 Figure A-2 Depth of Cut 0.05 in. Feed Rate 0.011 in/rev . 87 x
Figure A-3 Depth of Cut 0.06 in. Feed Rate 0.011 in/rev . 88 Figure B-1 Chip Dimensions Produced by 0.03 in. Depth of Cut and 0.011 in/rev Feed Rate . 89 Figure B-2 Chip Dimensions Produced by 0.05 in. Depth of Cut and 0.011 in/rev Feed Rate . 90 Figure B-3 Chip Dimensions Produced by 0.06 in. Depth of Cut and 0.011 in/rev Feed Rate . 90 Figure C-1 TNMG QF 333 4025 Insert Chip-Breaking Chart . 92 Figure C-2 TNMG QF 332 4025 Insert Chip-Breaking Chart . 93 Figure C-3 TNMG QF 332 4025 Insert Chip-Breaking Chart . 94 Figure C-4 TNMG 332K KC850 Insert Chip-Breaking Chart . 95 xi
List of Tables Table 4-2 Test Parameters for Machining . 46 Table 4-1 Insert Measurement Results . 47 Table 4-3 Calculated Results for TNMP 332K KC850 Insert. 48 Table 4-4 Results of CNMG432-NL92 Inserts Machining . 50 Table 5-1 Insert Geometric Parameters . 66 Table 5-2 Cutting Test Result . 67 xii
1 Introduction Machining chip-control has been overlooked in manufacturing process control for a long time. However, with the automation of manufacturing processes, chip-control becomes an essential issue in machining operations in order to carry out the manufacturing processes efficiently and smoothly, especially in today’s unmanned machining systems and finishing operations. On the three main areas of chip control study include chip formation, which covers chip flow and chip curl, and chip-breaking many experiments have been conducted. However given the complicated nature of chip formation, breaking and the progressive insert groove production, the results obtained from analysis do not match with industrial expectations. This chapter gives an overview in two categories; chip formation and chip breaking. 1.1 Overview of Chip Formation After material is removed from the workpiece, it flows out in the form of chips. After flowing out, the chip curls either naturally or through contact with obstacles. The most logical approach in developing cutting models for machining with chipbreaking is first to investigate and understand the direction of chip flow, since chip curling and the subsequent chip-breaking processes depend very heavily on the nature of chip flow and its direction. For chip flow study, the most important objective is to establish the model of the chip side-flow angle, which in most research is called the chip flow angle. Figure 1-1 shows chip side flow angle. 1
Figure 1-1 Chip Side Flow Angle (Stabler 1964) Naturally a chip will curl after it flows out. Contact with the chip-breaking groove or chip breaker or other obstacles will also make a chip curl. There are three basic forms of chip curl, and combinations of these construct all chip shapes: Chip up-curl Chip side-curl Chip lateral-curl that was found in recent studies The chip curl study requires the modeling of the chip up-curl and side-curl radii, both of which have very significant influences on chip-breaking. Figure 1-2 shows chip up-curl and side-curl. a) Chip Side-Curl b) Chip Up-Curl Figure 1-2 Chip Side-Curl and Chip Up-Curl (Spaans 1971) 2
1.2 Overview of Chip Breaking In machining chips that vary in shape and length, short broken chips are desired because: Operator’s safety (in manual operation) Safety of machine tools and cutting tools Maintaining good surface finish on the machined surface Convenience of chip disposal Reduction of cutting temperature Increasing tool life and Possible power reduction Therefore the study of chip-breaking is very important for optimizing the machining process. This importance is more significant in ductile materials such as soft gummy low carbon, tough steels leaded or resulfurized steels, and other soft materials and light cuts with positive rake angle tools. Efficient chip-control will contribute to higher reliability of the machining process, a better-finished surface, and increased productivity. Chip-breaking for brittle and ductile materials happen in different ways. When brittle metal such as cast iron and hard bronze are cut discontinuously segmented chips are produced naturally. As the point of the cutting tool contacts the metal, some compression occurs, and the chip begins flowing along the chip-tool interface. As more stress is applied to the brittle metal by cutting action, the metal compresses until it reaches a point where rupture occurs and the chip separates from the unmachined portion. This cycle is repeated indefinitely during the cutting operation, with the rupture of each 3
segment occurring on the shear angle or plane. Generally, as a result of these successive ruptures, a poor surface is produced on the workpiece. Figure 1-3 Chip Breaking in Brittle Materials In each cycle of ductile materials chip breaking, a chip first flows out with some initial curling. Then the chip will keep on flowing out until it comes into contact with (simultaneously blocked by) obstacles like the work-piece surface or the cutting tool. The chip curl radius will then become larger and larger with the chip continuously flowing out. When the chip curl is tight enough to make the chip deformation exceed the chip material breaking strain, the old chip will break, and new chips will form, grow and flow out (see Figure 1-4). Figure 1-4 Chip-Breaking of Ductile Materials (Shinojukza, 2001) Therefore the chip will break when the actual chip fracture strain (ε) is smaller than the tensile strain of the chip (εB), The chip-breaking research includes many components and activities including: Workpiece material Tool geometry (including chip breaker features) 4
Process parameters (built-up edge, vibration, force, heat, tool wear) Cutting condition (feed rate, depth of cut, cutting speed) Coolant Figure 1-5 shows the main scope of chip-breaking study. Its goals are to: establish a chip-breaking model for prediction, design machining process, select tool, and design tool. Figure 1-5 Research Fields of Chip-Control (Zhou 2001) To break chips by mechanical obstacles there are two main chip-breaking modes: chip-breaking by chip/work-surface contact and chip-breaking by chip/tool flank-surface contact (Figure 1-6). In the first mode a chip may break by contact with the surface to be machined, which is caused by chip side-curl (Figure 1-6e). It can also, break by contact with the machined surface (shoulder of workpiece) caused by chip up-curl (Figure 1-6a, 5
1-6b). The second breaking mode chip breaks by contact with the flank-surface caused by both chip up (Figure 1-6c) and side curl (Figure 1-6d) Figure 1-6 Modes of Chip Breaking (Nakayama 1960) In this thesis the chip-breaking in up-curl chips is studied, and later on this type of chip formation and breaking will be analyzed in detail. There are three major factors that affect chip breaking: Change cutting conditions (feed rate, depth of cut, cutting speed) Change cutting tool geometric features (nose radius, rake angle, lead angle) 6
Design and use a chip breaker or chip-breaking groove (groove width, backwall height, backwall angle) Increasing the depth of cut or the feed rate can significantly improve chip breakability. However, in industry this is not practical in finish cutting due to the limitations of the machining process. Therefore, optimizing the design of the cutting tool’s geometric features and the chip breaker / chip-breaking groove is the most plausible and efficient way to break the chip. 7
2 Literature Review of Chip Formation and Breaking This chapter reviews both previous work done by researchers on fundamentals of chip-formation and breaking, and attempts to develop chip-breaking criteria. The Nakayama’s chip-breaking criterion, and Li’s work on chip-breaking limits are reviewed in detail. This is particularly important because the chip-breaking predictive models developed in this thesis are based on chip-breaking limits theory and on Nakayama’s work. Finally, existing problems in chip-control and formation models are also reviewed. 2.1 Chip Flow Chip-breaking modes depend on the nature of chip flow and its direction. Understanding the chip flow mechanism is important for chip-control. Chip flow is determined by many factors and is usually described by the chip flow angle (ψλ). The chip-flow angle is the angle between the chip-flow direction on the cutting tool rake-face and the normal line of the cutting edge (see Figure 2-1). Establishing the model of the chip flow angle is the main objective of chip flow research. Due to the extreme complexity of the chip formation process, only limited success has been achieved in chipflow research, especially in three-dimensional conditions (three-dimensional groove, and three-dimensional cutting). A lot of work has been done on chip-flow angle research during the last few decades, and there are many methods for calculating the chip-flow angle. The investigation of chip flow began with modeling over plane rake face tools. 8
Figure 2-1 Chip Side Flow Angle (Jawahir, 1993) Merchant, Shaffer and Lee used the plasticity theory to attempt to obtain a unique relationship between the chip shear plane angle, the tool rake angle and the friction angle between the chip and the tool (Merchant, 1945; Lee, 1951). Shaw (1953) proposed a modification to the model presented by Lee and Shaffer. Palmer (1959) presented the shear zone theory by allowing for variation in the flow stress for a work-hardening material. Van Turkovich (1967) investigated the significance of work material properties and the cyclic nature of the chip-formation process in metal cutting. Slip line field theory is widely applied in chip-formation research and some slip-line field models are presented (Usui, 1963; Johnson, 1970; Fang, N. 2001). Being computationally successful, slip line field models do not agree well with experiment results due to lack of knowledge of the high strain rate and temperature flow properties of the chip material. Through studying the chip flow in free oblique cutting, Stabler presented a famous rule called the “Stabler Rule”
Nomenclature bch Chip width (mm), (in) bγ1 Insert/chip restricted contact length (mm), (in) Ch Cutting ratio (the ratio of the undeformed chip thickness to the chip thickness) d Depth of cut (mm), (in) d0 The standard critical depth of cut under pre-defined standard cutting condition (mm), (in) dmax Maximum depth of cut in extra region of chip-breaking chart (mm), (in)
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